Improve documentation of installing SDL and SDL2

Remove how to install SDL1 / SDL2 from var.mk as it's already in faq.md.
Instead refer to faq.md. How to compile (variables etc.) is still in the
var.mk file.

Reworded that section a bit and added 'Other linux distributions'
subsection to 'Linux' (in faq.md).

Minor typo fix in faq.md at the same time as the above change. Normally
I would not do this but it's one word changed and I am too tired at this
time (or can't be bothered?) to do another pull request for one word.

faq.md

@@ -68,8 +68,9 @@ applications.
 
 ## Q: How do I compile and run entries that use SDL1/SDL2 ?
 
-This depends on your operating system but below are some instructions for some
-OSes.
+This depends on your operating system but below are instructions for linux and
+macOS with alternative methods for macOS and different package managers with
+linux.
 
 ### Red Hat based linux
 
@@ -121,10 +122,17 @@ but this might not be necessary in more modern days especially as we use
 `sdl-config` and `sdl2-config` which should find the proper paths.
 
 
+### Other linux distributions
+
+Use your package manager to install the appropriate packages. Try the search
+feature of the package manager to determine which packages you need to install.
+Note that you might have to install both the library and the developmental
+packages: one for compiling and one for linking / running.
+
 ### macOS
 
 If you're using macOS there are at least three ways to obtain it. You can
-download it from the SDL website and install the package. This will possibly not
+download it from the SDL website and install the package. The latter will not
 work well for the IOCCC but these will:
 
 #### MacPorts
@@ -152,7 +160,7 @@ eval "$(/opt/homebrew/bin/brew shellenv)"
 
 As entries have been fixed it is entirely possible that some of the entries no
 longer fit within the year's size restrictions. Invariably the length of columns
-and number of rows might also be changed.
+and number of rows might also have changed.
 
 For the original version see the [/archive](/archive) directory where you can
 find all the original winning entries.

var.mk

@@ -282,40 +282,19 @@ X11_LIBDIR= /opt/X11/lib
 X11_INCDIR= /opt/X11/include
 
 
-############################
-# SD1 and SDL2 include files
-############################
-
-# macOS users:
+##########################
+# SD1 and SDL2 libraries #
+##########################
 #
-# If you have not aleady do so, install Homebrew.  See the following for information:
+# For details on how to install SDL/SDL2 see faq.md.
 #
-#	https://brew.sh
-#
-# Then to install SDL and SDL2, execute the following command:
-#
-#	brew install sdl2 sdl12-compat
-#	eval "$(/opt/homebrew/bin/brew shellenv)"
-
-# Linux users:
-#
-# To install SDL and SDL2, execute the following command as root:
-#
-#	dnf install SDL2 SDL2-devel sdl12-compat sdl12-compat-devel
-
-# Debian users:
-#
-# To install SDL and SDL2, execute the following command as root:
-#
-#	apt install libsdl1.2debian libsdl1.2-dev libsdl2-dev
-
 # SDL2_INCLUDE_ROOT is the directory under which include/SDL/ and/or
 # include/SDL2/ may be found.
 #
-# Even if you do not use HomeBrew, you might set the environment
-# variable $HOMEBREW_PREFIX to the SDL2_INCLUDE_ROOT directory path
-# as the default SDL2_INCLUDE_ROOT value is $HOMEBREW_PREFIX.
-# Of you may run make and set SDL2_INCLUDE_ROOT directly:
+# Even if you do not use Homebrew (one of the methods for macOS), you might set
+# the environment variable $HOMEBREW_PREFIX to the SDL2_INCLUDE_ROOT directory
+# path as the default SDL2_INCLUDE_ROOT value is $HOMEBREW_PREFIX.  Of you may
+# run make and set SDL2_INCLUDE_ROOT directly:
 #
 #	make all SDL2_INCLUDE_ROOT=/some/path
 #